Surface mount technology (SMT) is used for constructing electronic circuits where the components (surface-mounted components/SMCs) are mounted directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface mount device (SMD). SMT has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.
An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component.
Edge emitting lasers have beams that widen very fast in a direction normal to the mounting surface. Edge emitting lasers can be mounted in packages with leads that orient the laser perpendicular to the main driver board. The package must have a window cap or encapsulation to protect the laser which is placed at the edge of the lead frame or pedestal of the package base. When mounted on a large, flat surface, such as directly on the main driver board or on a secondary substrate which could be a PCB, ceramic or other substrate that is then mounted on the main driver board, at least a portion of the beam may intersect the surface. To overcome this limitation, edge emitting lasers are often mounted at the edge of a driver board or secondary substrate, where the edge of the laser is adjacent to or nearly adjacent to the edge of the board or substrate so the beam widens in an area beyond the board or substrate. Such an arrangement has several disadvantages. For example, the facet of a laser is typically sensitive to contamination and humidity, among other sensitivities, and the proximity to the edge of the board or substrate may increase the vulnerability of the facet. In addition, the necessity of locating the laser at the edge of a board or substrate limits the flexibility of board design, and may make certain packaging options impractical, for example, certain chip carriers, such as a laminate leadless carrier (LLC). A laminate leadless carrier uses flat metal pads that make contact with a printed circuit board. There are no pins extending out of the package and it may be mounted on the printed circuit board directly. A laminate leadless carrier includes multiple layers of conductive and dielectric layers laminated together.
While SMT provides advantages in manufacturing and circuit layout, the limitations of semiconductor edge emitting laser chips have provided a challenge to SMT lasers. Besides the logistical problems related to positioning a semiconductor laser chip at the edge of a surface mount package, thermal dissipation considerations may conflict with surface mount features. In particular, SMT generally makes it difficult to conduct heat generated by a semiconductor laser chip to the surface of the package, where it may be further dissipated, for example using heat sinks or convection methods.
Therefore, there is a need in the industry to overcome some or all of the above shortcomings.